The importance of achieving accurate mutual alignment of individual components in any optical system is well known. The miniature dimensions of components used in modern optical communication systems render such alignment difficult both to achieve and to maintain. For example, one problem in the construction of laser transmitters is that of efficiently coupling the optical output from a laser diode into an optical fiber. To obtain efficient coupling, the fiber end is desirably precisely aligned with the emitting area of the laser. When such an alignment is achieved, the fiber is then fixed in place, ideally by a method that ensures alignment is sustained throughout the device lifetime.
Typically, precise alignment of the fiber involves aligning the end of the fiber in at least one direction relative to the optical device to provide a maximum energy transfer from the optical device to the fiber. A further optical device such as a photodiode may be used to measure optical power coupled into the optical fiber. The fiber may be adjusted in vertical and lateral alignment until a maximum power coupling is achieved. A predetermined gap distance may be used for horizontal alignment or the gap distance may be adjusted while visually monitoring the distance to avoid direct contact between the fiber and the optical device.
It is typically difficult, however, to determine an optimal gap distance. Even if visual means are used, the resolution of cameras or other monitoring devices available may not be sufficient to allow accurate determination of an optimal coupling position. The resolution of the image may also make the position of the edge of the fiber and/or the optical device difficult to determine. This uncertainty may result in a premature contact between the fiber and the optical device or in the optical device being separated from the optical fiber by too large a gap.